Rotary potentiometer with fine adjustment

ABSTRACT

A miniature potentiometer of high accuracy comprises a support carrying an electrically resistive component extending about a support axis; a rotatable contact in wiping engagement with the component; a rotary member carried by the support to be rotatably adjusted; rotary gearing including sun, planet and ring gears to transmit rotation between the member and contact with mechanical advantage: and electrical terminals.

United States Patent Akashi May 22, 1973 ROTARY POTENTIOMETER WITH FINEADJUSTMENT 3,533,042 10/1970 Casey et al. ..338/162 PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-D. A. ToneAttorney-William W. Haeflinger et al.

[5 7] ABSTRACT .A miniature potentiometer of high accuracy comprises asupport carrying an electrically resistive component extending about asupport axis; a rotatable contact in wiping engagement with thecomponent; a rotary member carried by the support to be rotatablyadjusted; rotary gearing including sun, planet and ring gears totransmit rotation between the member and contact with mechanicaladvantage: and electrical terminals.

7 Claims, 4 Drawing Figures ROTARY POTENTIOMETER WITH FINE ADJUSTMENTBACKGROUND OF THE INVENTION This invention relates generally topotentiometers, and more particularly concerns advances in the art ofprecision calibration adjustment of miniature potentiometers.

Modern circuitry compactness requires miniature components includingpotentiometers. Particularly is there need for highly accuratepotentiometers of overall diameter less than about one-fourth inch.However, the demands of reduced size are in conflict with therequirements of high accuracy, since for example, reducing the length ofthe resistance component in a potentiometer normally results indiminished accuracy. Other requirements such as vibration and waterproof construction are increasingly difficult to meet as the size of thepotentiometer is reduced SUMMARY OF THE INVENTION It is a major objectof the invention to provide a solution to the above requirements as wellas others, the improved potentiometer characterized by unusualadvantages, in construction, mode of operation and results. Theseinclude a design enabling increasing miniaturization without destroyingaccuracy; waterproof, dustproof and vibration proof construction; a geartrans mission that enables accurate adjustment; maximum resistor lengthand ease of fabrication of the resistor component; and consistent anddependable operation.

Basically, the potentiometer comprises a support means (as may includebody and enveloping cover elements) defining a main axis and aresistance component extending about that axis (as for example withfrusto-conical configuration); a rotatable electrical contact havingwiping contact with the resistance component; a rotary adjustment membercarried by the support means; rotary gearing connected to transferrotary motion from the adjustment member to the contact and withmechanical advantage for calibration accuracy, as will be seen; andthree electrical terminals respectively connected with the contact andspaced portions of the resistance component.

Typically, the gearing will include a sun gear connected with theadjustment member; planet gear means rotated by the sun gear and aboutfixed axes spaced from the main axis; and a ring gear arranged to berotated about the main axis by the planet gear means, to rotate thecontact at a substantially slower angular velocity than the angularvelocity of the adjustment member. Further, the location and arrangementof these elements in relation to the remainder of the potentiometerenables extreme overall miniaturization, as will be seen.

Additional features include the carriage of the wiping contact by thering gear at the side thereof opposite the planet and sun gear elements,and in such manner as to assure firm yieldable engagement of the contactwith the resistance component in frusto-conical form for maximum length;and O-ring seals are located to benefit from compression in response tosimple assembly of the cover into the body, as will be seen.

These and other objects and advantages of the invention, as well as thedetails of an illustrative embodiment, will be more fully understoodfrom the following description and drawings, in which:

DRAWING DESCRIPTION FIG. 1 is an elevation taken in section through apotentiometer embodying the invention;

FIG. 2 is a horizontal section taken on lines 2-2 of FIG. 1;

FIG. 3 is a top plan view of the FIG. 1 potentiometer; and

FIG. 4 is a fragmentary plan view of the wiper contact seen in FIG. 1.

DETAILED DESCRIPTION In the drawings, the potentiometer 10 is seen toincorporate support means such as may include body and cover elements 11and 12. The body may consist of ceramic material, while the cover mayconsist of metal such as press steel, and may receive the body as shown,these elements defining a main axis 13.

An electrically resistive component is carried on the support means toextend arcuately about that axis; in particular, the resistive componentmay consist of a thin strip 14 (as for example silver base paint withresistive particles; as known) rolled into the frusto-conical body face15 to itself define a frusto-conical arcuate surface 14a. The latter isengaged by a rotatable electrical contact 16 at the side of body 11exerting pressure against the surface 14a, the contact consisting forexample of beryllium copper. The contact also includes a fiat spring armsection 16a extending over the top of body 11, and bowed downwardly asshown to forcibly engage the conductive terminal plate 17 seated in arecess 18 in the top of body 11. Terminal pin 19 is solder connected toplate 17 and projects through and below the body to provide externalelectrical connection with confined wiper contact 16; and, terminal pins20 and 21 are connected by soldering with the arcuately spaced endportions of the resistive component 14, i.e., at locations 20a and 21a,these pins also projecting below the body.

A rotary member 23 is carried by the support means to be rotatablyadjusted, as by turning of a screw driver the tip of which fits in slot24, in order to effect desired adjustment of the resistancecharacteristic of the potentiometer. The member 23 has successivesections 23a23d, as shown, section 23a received through an opening 25through the cap or cover boss 12a, and section 23d seating on plate 17.Pressurally confined between flange section 23b and the cover is anelastomer O-ring 26 sealing off there between for dust and waterproofprotection of the confined wiper contact and resistive component.Another O-ring 27 seals off between the lower skirt portion 28 of thecover and the body 11 to complete the dust free and water proofprotection, and portion 28 is crimped inwardly during assembly todevelop endwise force retaining the cap or cover on the body andpressurizing the O-ring 27.

In accordance with an important feature of the invention, rotary gearingis provided to be carried by the support means and connected to transmitrotation between the member 23 and the contact 16, and with mechanicaladvantage. As a result, turning of member 23 through a given angleresults in rotary displacement of contact 16 through a substantiallysmaller angle, and typically less than one-fourth the given angle,producing greatly enhanced fine adjustment capability (or resistivecalibration) of the potentiometer as compared with devices whereinadjustment and wiper elements are characteristically displaced throughequal angles. Thus the member 23 may be revolved several times in orderto displace the wiper contact through its complete range of engagementwith the C-shaped resistance component 14.

In the example shown, the gearing includes a sun gear 30 on section 230of member 23; planet gear means, as for example three planet gears 31meshing with the sun gear and to be rotated about fixed axes 32 spacedfrom axis 13; and an internal ring gear 33 meshing with the planet gearsand carried to be rotated about main axis 13 in response to planet gearrotation. The ring gear extends at 3311 beneath the planet gears tosupport same, the planet gears having annular configuration with coveroffsets 34 received by the planet gears to locate them for rotation.

A guide slot 35 in the underside of ring gear section 33a receives thewiper contact bowed arm 16a, as shown. The construction is such thatwhen the cover is assembled to the body, the arm 16a is yieldably urgedagainst plate 17 for firm electrical contact, and also the contact 16 isyieldably and firmly urged inwardly against the resistive component 14,as described.

All gearing and the member 23 may advantageously consist of dielectricplastic material. Also, as seen in FIG. 2, body 11 may have a locatingflat 50 at one side thereof. Terminal pins 19, 20 and 21 may be stakedin place at 51-53 on the body. Contact 16 may have a local V-shapedcross section adjacent component 15 as seen in FIG. 4, for rigidity andassurance of firm engagement with that component.

It should be noted that all moving parts as described are rotatableabout axis 13, insuring accuracy and dependability of the potentiometer.Also, the resister 14 may alternatively comprise a copper wirerectangularly wound to form flat coils bonded to frusto-conical surface15 of body 11, as for example by epoxide bonding agent.

I claim:

1. A potentiometer comprising a. support means defining a main axis andan electrically resistive component on said means and extendingarcuately about said axis,

b. a rotatable electrical contact having Wiping engagement with saidcomponent,

c. a rotary member carried by the support means to be rotatablyadjusted,

d. rotary gearing carried by the support means and connected to transmitrotation between said member and contact and with mechanical advantage,

' said gearing including a sun gear directly connected with said rotarymember, planet gear means engaging the sun gear to be rotated about atleast one fixed planet gear axis spaced from the main axis, and a ringgear carried by the support means to be rotated about the main axis bythe planet gear means and to rotate the contact, and

e. three electrical terminals one of which is electrically connectedwith the contact, and the other two of which have electrical connectionwith arcuately spaced portions of said component.

2. The potentiometer of claim 1 wherein the contact includes a flatspring section carried by the ring gear and urged thereby to yieldablyengage said component.

3. The potentiometer of claim 2 wherein the component has afrusto-conical outer surface engaged by the contact.

4. The potentiometer of claim 2 wherein the ring gear is grooved toreceive the flat spring section in bowed configuration to yieldablyengage a terminal plate on a body element, the ring gear rotating on astem portion of the rotary member.

5. The potentiometer of claim 4 wherein the gear consists of dielectricplastic material; the body consists of ceramic, and the cover consistsof metal.

6. The potentiometer of claim 1 wherein said support means includes bodyand cover elements, said component carried by the body and enveloped bythe cover, and the cover carrying said gearing.

7. The potentiometer of claim 6 including O-rings sealing off betweenthe body and cover and between the cover and said member, the coverdefining an axial opening in which said member extends.

* i I! 1R

1. A potentiometer comprising a. support means defining a main axis andan electrically resistive component on said means and extendingarcuately about said axis, b. a rotatable electrical contact havingwiping engagement with said component, c. a rotary member carried by thesupport means to be rotatably adjusted, d. rotary gearing carried by thesupport means and connected to transmit rotation between said member andcontact and with mechanical advantage, said gearing including a sun geardirectly connected with said rotary member, planet gear means engagingthe sun gear to be rotated about at least one fixed planet gear axisspaced from the main axis, and a ring gear carried by the support meansto be rotated about the main axis by the planet gear means and to rotatethe contact, and e. three electrical terminals one of which iselectrically connected with the contact, and the other two of which haveelectrical connection with arcuately spaced portions of said component.2. The potentiometer of claim 1 wherein the contact includes a flatspring section carried by the ring gear and urged thereby to yieldablyengage said component.
 3. The potentiometer of claim 2 wherein thecomponent has a frusto-conical outer surface engaged by the contact. 4.The potentiometer of claim 2 wherein the ring gear is grooved to receivethe flat spring section in bowed configuration to yieldably engage aterminal plate on a body element, the ring gear rotating on a stemportion of the rotary member.
 5. The potentiometer of claim 4 whereinthe gear consists of dielectric plastic material; the body consists ofceramic, and the cover consists of metal.
 6. The potentiometer of claim1 wherein said support means includes body and cover elements, saidcomponent carried by the body and enveloped by the cover, and the covercarrying said gearing.
 7. The potentiometer of claim 6 including O-ringssealing off between the body and cover and between the cover and saidmember, the cover defining an axial opening in which said memberextends.